1. Field of the Invention
The present invention relates to an intake device of an internal combustion engine.
2. Description of the Related Art
In a known engine having a butterfly valve within a surge tank, the interior of the surge tank is divided into a first interior chamber and a second interior chamber by the butterfly valve when the butterfly valve is completely closed, and the first interior chamber and the second interior chamber are interconnected when the butterfly valve is fully open (see, for example, Japanese Unexamined Patent Publication No. 56-115818). In this engine, to obtain a high volumetric efficiency over the entire range of an engine speed by using an air pulsating operation, the equivalent pipe length of the intake passage is changed in accordance with an engine operating state by fully closing or fully opening the butterfly valve. However, in this engine, if only a small amount of air leakage occurs at the butterfly valve when the butterfly valve is fully closed, the air pulsating operation is weakened, and thus it is impossible to obtain a desired high volumetric efficiency. Consequently, in this engine, when the butterfly valve is fully closed, a tight seal is required for the butterfly valve, although the butterfly valve per se already has a good sealing ability.
Nevertheless, when the butterfly valve is actually arranged in the surge tank, the machining of the valve seat for the butterfly valve is difficult and the assembling of the butterfly valve in the surge tank is also difficult. Consequently, although the butterfly valve is very suitable for an air pulsating system, a special arrangement becomes necessary to obtain a good sealing operation and an easy assembling of the butterfly valve. Therefore, to obtain such a good sealing operation and easy assembling, an intake device is known in which a valve holder holding the butterfly valve therein is formed separately from the surge tank and fitted into a cutaway portion formed in the surge tank (see, Japanese Unexamined Utility Model Publication No. 61-48923).
However, in this intake device, the valve holder is merely fitted into the cutaway portion of the surge tank, and thus a clearance is formed at the mating face of the valve holder and the cutaway portion. As a result, since air will leak through this clearance, the air pulsating operation is weakened, and a problem arises in that it is impossible to obtain a desired high volumetric efficiency.